The invention relates to pharmaceuticals, and more particularly relates to pharmaceuticals for treating tumors in humans. In its most immediate sense, the invention relates to bioactive ribonucleases (“RNases”).
Some RNases are known to be active against certain human tumor cells. For example, commonly-owned U.S. Pat. No. 5,559,212 discloses and claims ranpirnase, an RNase pharmaceutical that is presently known by the registered trademark ONCONASE and that is presently the subject of Phase III clinical trials. And, commonly-owned U.S. Pat. No. 6,239,257 B1 discloses four RNase proteins that belong to the pancreatic RNase A superfamily, each possessing activity against two human carcinoma cell lines.
Attention is now being directed to “targeting” pharmaceuticals to deliver them to particular cell receptors of interest. This is accomplished by selecting a targeting moiety that is preferentially attracted to the desired cell receptor and attaching (as by conjugation or fusion) the targeting moiety to the pharmaceutical.
Commonly-owned U.S. Pat. No. 6,175,003 B1 discusses the concept of targeting therapeutically active RNases by “cysteinizing” them. In the case of ranpirnase, this can be accomplished by conjugating the targeting moiety to the cysteine residue at position 72. While this approach is promising and is still under investigation, some people believe that it may be difficult to obtain regulatory approval for a conjugate and that a fusion protein would have an easier path to regulatory approval.
The N-terminal residue of ranpirnase is pyroglutamic acid. This “blocks” the N-terminal, i.e. makes it impossible to attach other amino acid residues to the left of the N-terminal. For this reason, it is not possible to create a fusion protein by attaching a targeting moiety to the N-terminal of ranpirnase. And, while it is possible to remove the pyroglutamic acid residue and to attach a targeting moiety to the aspartic amino acid residue in the second position of ranpirnase, removal of the pyroglutamic acid residue eliminates the bioactivity of ranpirnase.
However, the RNases disclosed in the above-referenced U.S. Pat. No. 6,239,257 B1 are not only active against certain human cancer cells, but also lack “blocked” N-terminals. For this reason, each of these RNases could be used to make a targeted fusion protein by attaching a targeting moiety to its N-terminal end.
It would be advantageous to provide methods for manufacturing such proteins recombinantly.
It would further be advantageous to provide bioactive proteins that could be made into targeted fusion proteins.
In accordance with one aspect of the invention, methods are provided for recombinantly manufacturing the proteins disclosed in U.S. Pat. No. 6,239,257 B1.
In accordance with another aspect of the invention, new proteins are provided that possess activity against human carcinoma cells and that can also be manufactured recombinantly. One of the proteins is “cysteinized” to permit easier conjugation to a targeting moiety.
When recombinantly manufactured, one of the proteins disclosed in U.S. Pat. No. 6,239,257 B1 retains its activity against human carcinoma cells even when a number of different leader sequences are attached to its N-terminal. The leader sequences form parts of the vector in which the DNA of the protein of interest has been inserted. As will be seen below, there is a compelling body of evidence that such leader sequences do not, when attached to the N-terminal of any one of the family of RNase proteins disclosed in U.S. Pat. No. 6,239,257 B1, affect the bioactivity of the protein.